James henry macmahon



Patented Nov. 20, 1923.

UNITED STATES PATENT OFFICE.

JAMES HENRY MACMAHON, 0F SALTVILLE, VIRGINIA, ASSIGNOR, TO THE MA'I'HIESON ALKALI WORKS, INC., 0]? NEW YORK, N. Y., A CORPORATION OF VIRGINIA.

MANUFACTURE OF BLEACHING-POWDER SOLUTIONS.

ll'o Drawing.

To all whom. it may concern:

Be it known that I, J AMES H. MAoMAHoN, a citizen of the United States, residing at Saltville, in the county of Smyth, State of Virginia, have invented certain new and useful Improvements in the Manufacture of Bleaching-Powder Solutions; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to improvements in the manufacture of stable and neutral or substantially neutral solutions of bleaching powder, and includes the solutions themselves as well as the improved method of their manufacture.

Bleaching powder of standard commercial quality contains about thirty-five per cent available chlorine, this percentage varying somewhat and running sometimes as high as thirty-nine per cent and occasionally as low as thirty-two per cent. It also contains free lime in appreciable amount, as a hydrated lime, the amount ordinarily being from about six to fourteen per cent. In the manufacture of solutions of the bleaching powder for use, the bleaching powder is commonly added to water. in proportions to form a solution containing about 20 grammes of available chlorine per litre, although this amount may vary somewhat. The bleaching powder and water are then agitated together in tanks and then theexcess a hydrate lime and small proportions of other insoluble materials are allowed to settle, and the clear liquor is drawn of! as completely as possible, and forms the bleach solution.

In the manufacture of bleach solutions in this way, the rate of settling of the insoluble material from the solution varies greatly with different kinds of bleaching powder.

The particles of hydrated lime are often so fine that settling may require many hours standing. Some limes seem to contain the hydrated lime in a more or less colloidal state, so that the bleaching powder solutions containin the excess lime, will have a more or less co loidal character, or it may be that the colloidal character which makes settling so difiicult ma be due to othersubstances, such as alumina or perhaps silicic acid.

After the settling operation has been com- Serial No. 525,689.

pleted, and the clear bleach liquor has been drawn off, the lime sludge will still retain some of the bleach solution, and the lime sludge must then be stirred up with fresh water and settled again, in order to extract the bleach solution which it retains. The resulting bleach solution obtained in this washing operation is quite dilute. Furthermore, there remains a considerable amount of lime sludge which must ultimately be disposed of in some manner, and this disposal may add to the expense of producing the bleach solution, while the accumulation of the lime sludge prior to its removal is a nuisance wherever bleaching powder is used in the manner above mentioned.

Bleaching solutions produced as above described commonly have an alkaline reaction, and it is quite commonly believed (and statements to this effect are frequently found in the literature) that bleaching solutions must be markedly alkaline in order to be stable.

The present invention avoids or overcomes the objections and difliculties above mentioned in the settling of the excess lime from the solutions and in the washing and disposal of the lime sludge, and it provides an improved bleaching solution which is neutral or substantially neutral in character, but which is, nevertheless, stable.

According to the present invention, the bleaching powder, which may be the ordinary commercial bleaching powder, is mixed with water, for example, in about the usual proportions, and, without waiting for the solution to settle, chlorine is passed into the solution until practically all of the free lime has been acted upon by the chlorine to form more chloride and/or hypochlorite in solution. I have found, contrary to the common belief, that the lime in the bleaching powder solution can be converted by the chlorine into chloride and/or hypochlorite and that the resulting solution, although substantially free from lime, and neutral or approximately so, is nevertheless, quite stable.

I have also found that, when the alkalinity of the solution due to free lime is reduced to a very small minimum or trace, the resulting bleaching solution is more rapid in its action, and also more efiicient, and can accordingly be used to better advantage for bleaching purposes. The bleaching solution is, therefore, distinguished in its action from ordinary alkaline bleaching solutions,

which are slow acting and which, owing to the rapidity of ordinary commercial bleaching, are not allowed suflicient time to accomplish the full bleaching effect.

In producing the new bleaching solution, the chlorine may be introduced in any suitable manner, which will bring it into intimate contact and reaction with the excess lime which the solution contains. The chlorine can be introduced, for example, through a tube or pipe perforated with small holes for breaking up the chlorine into small gas bubbles, or through a so-called diiiuser consisting of a tube or plate of porous material such as baked silica, alumina, porous clay, or other similar material through which gaseous chlorine will be introduced in very tine, small bubbles, so that the chlorine will be readily absorbed by the solution. The solution may be agitated to assist in keeping the finely divided particles of lime in suspension and insuring that they are made to react with the chlorine introduced. The liquid bleach mixture containing the excess milk of lime may also be circulated through a tower containing chlorine gas, and thus brought into contact with the chlorine, although, in practice, the introduction of the chlorine through a perforated pipe or porous medium into the solution appears to be better. The alkaline bleach solution may also be sprayed through a closed tower or chamber containing gaseouschlorine. Preterably a wooden apparatus is used in the chlorine treatment, although metal apparatus, made of metal resistant to corrosion by the chlorine and chlorine compound, may be used. Cement or brick lined tanks may also be used.

The invention will be "further illustrated by the following typical examples, but it will be understood that the invention is not limited thereto:

A sample of good commercial bleaching powder, containing 36.9 per cent available chlorine and 13 per cent of hydrated lime was mixed. with water to form a mixture or partial solution containing 20.7 grammes of available chlorine per litre. Chlorine gas was then passed into the solution in the form oi tine bubbles, and with agitation of the solution, until the tree lime was substantially consumed. The solution was then found to contain 28.4 grammes of available chlorine per litre, and, after standing for sixteen hours the solution tested 28.3 grammes of available chlorine per litre, thus indicating that the solution was quite stable 1n character, although the free lime had been substantially consumed in the chlorinating treatment.

Another lot of bleaching powder containmg 38.4 per cent available chlorine and 7 per cent hydrated lime, was made up with water to a solution containing 20.7 grammes available chlorine per litre. Chlorine was then passed in until the lime was substantially consumed. The resulting solution showed 25.6 grammes available chlorine per litre, and the solution was quite stable in character, although the solution was substantially free from lime, and therefore, neutral or approximately so, in character.

In the chlorination of the solution there is relatively little heating caused by the reaction, so that it is not necessary to cool the solution. The operation can be carried out at ordinary atmospheric temperatures or between fifteen and twenty-five degrees C.

The treatment of the bleaching powder solution in the manner above described enables the excess of free lime of the bleaching powder to be utilized in the production of additional bleach, thus increasing the amount of effective bleaching agents in the solution, as well as increasing the strength of the bleaching solution. The utilization of the tree lime in this way overcomes the troublesome settling problems involved in making the ordinary bleaching solution, inasmuch as the lime is dissolved by the chlorine treatment so that it does not require to be settled and separated as a lime sludge. Such residual insoluble matter, other than lime, as the solution may contain, is ordinarily very small in amount and settles very quickly. In fact, the clearing up of the solution as the result of the treatment with chlorine, takes place quickly and is readily observed, thus iving a visual indication of the reaction. wing to the greatly reduced amount of sludge which is formed and the ease with which the settling takes place, the separation of the bleach solution from the sludge presents little diificulty, while there is no waste of lime with the sludge and no difiiculty due to lime contained'in thesludge. The troublesome washing of the sludge is thus eliminated, and, instead of obtaining a wash water containing dilute bleach liquor, which, if added to the main bleach solution would correspondingly dilute it, the process of the present invention materially increases the concentration of the solution in terms of available chlorine or of bleaching chlorine. The resulting bleaching solution is moreover, as above pointed out, a stable solution, although practically free from free lime and from any appreciable alkaline reaction.

I claim:

1. The method of producing a bleaching solution which comprises mixing bleaching powder containing excess lime with water and treating the resulting mixture with chlorine.

2. The method of producing a bleaching solution which comprises mixing bleaching powder containing excess lime with water and treating the resulting mixture with chlorine, the amount of chlorine being sufficient to combine with practically all of the excess lime, whereby a bleaching solution is produced, substantially free from lime.

3. The method of producing a bleaching solution which comprises mixing bleaching powder containing excess lime with water and treating the resulting mixture with chlorine in sufficient amount to combine with 10 practically all of the excess lime and to give a solution from which remaining insoluble material will readily settle, settling the remaining insoluble material and separating the clear bleach solution therefrom.

4. A solution of bleaching powder of a stable character, which is substantially free from excess lime and from any markedly alkaline reaction.

In testimon whereof I affix my signature.

JA ES HENRY MACMAHON. 

